Cathode



CATHODE Filed Sept. 12-

f f 7J .Ivl .1. f 4 x lit lll l A n Patented Sept. 28, 1943 CATHODE Arthur K. Wing, Jr., Chatham, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 12, 1942, Serial No. 458,078

9 Claims.

My invention is directed to cathodes, particularly to filamentary cathodes for electron discharge devices of the high power or transmitter class.

The usual springs for tensioning cathode filaments are impractical in' some tubesr where the filaments are relatively heavy wires or rods, where there is limited space for the springs, and where the operating and/or exhaust temperatures are so high that metals are annealed and lose their springiness. The usual cathode constructions are particularly impractical in high power tubes with closely spaced electrodes and where multi-phased cathode power is desired. Bowing and shifting of the filaments are diiiicult to control when caused by strong magnetic fields produced by the heating current and by thermal expansions.

An object of my invention is an improved filamentary cathode for power tubes.

A more specific object oi' my invention is a multi-phase iilamentary cathode for power tubes which will rigidly hold its position with respect to the other electrodes in the tube and which will not change in size or shape.

The characteristic features of my invention are defined in the appended claims and one embodiment thereof is described in the following specication and shown in the accompanying drawing in whlch- Figure 1 shows the outline of one type of power tube in which my improved cathode may be advantageously employed;

f Figure 2 is an enlarged perspective View of my improved cathode;

Figure 3 is a plan View of one of the iillament spacers of `my improved cathode;

Figure 4 shows one wire anchor of the type usedin Figures 21and 3; and K Figure 5 is a detail view of the filament-toconnector junction.

The envelope of the power tube shown in `Figure 1 comprises the anode I Joined at its upper end in the glass bulb 2 and to a header through which lead-in conductors 3 are sealed. Concenrically within the anode is a cathode 4, and one or morey grids 5. Because of the extreme temperatures and voltages used during operation, ceramics or other insulators cannot be employed to space the electrodes at their lower ends. Hence the electrodes must be mounted with suiiicient rigidity at their upper ends to prevent lateral movement and changes in the normally small spacings between electrodes. important that a lateral movement of the fila- It is particularly l (Cl. Z50-27.5)

ment be prevented notwithstanding the considerable expansion of the filamentwhen heated from room temperature to an operating temperature of say 2300 C.

My improved cathode comprises parallel, cylindrically arranged filament wires or rods 6. The filament rods are straight and extend throughout 'the useful length of the tube and are so mounted that they are free to expand lengthwise, rbut are securely anchored against lateral movement. A support post 'l is rigidly secured to one of the conductors 3 at the upper end of an envelope and extends along theaxis of the cathode cylinder,`and terminates short of the lower end of the cylinder of filament rods. Spaced along the rods are one or more spacers or insulator discs 8, the holes through thecenters of the discs, through which the post passes, being large enough so that the discs may slide freely along the post. V-shaped Wire braces 9 secure each filament wire to each insulating disc, the bight of the wire being connected to the lament and the ends of the legs of the wire being connected to circumferentially spaced points on the disc. Each filament is thus anchored against movement toward or away from the supporting posts, as well as in a circumferential direction with respect to the discs and to each other. Each Wire may conveniently be attached to its iilament by looping the wire around the filament at the apex of the V, and the legs of the wire may be passed through pre-formed holes in the insulator and clinched as shown. Each wire then has considerable flexibility in a direction parallel to the axis of the filament rods.

Electrical connections are made between the ends of the filaments by thin sheet metal connectors I0, each connector having legs H extending outwardly to the end of the filaments. Each connector leg may have a loop or a fold to which the end of the filament is attached. The filaments are preferably of uniform length, for uniform heating current, and the length of the folds in the connector legs is adjusted longitudinally of the cathode to meet the filaments. Each ccnnector has considerable strength to resist movement of the filament in any radial direction, but is suiciently flexible to oler no resistance to lengthwise movement of the filaments. Where the cathode is'to be heated by three-phase power, the filaments are arranged in three groups and the filaments of each groupA connected to one connector. The three connectors for the three groups of filaments are preferably spaced lengthwise of the cathode as shown and are provided with folds of the proper length to'meet the ends of the laments. If desired the ends of the rilaments may be clamped between the folded ends of the connectors and small metal clips l2 snapped over the looped ends of the connectors. To insure good electrical and mechanical connections, the legs of the connectors, the clips and the laments may be arc welded at the free end. The filaments of my improved cathode are free to expand longitudinally, yet each filament Wire is rmly anchored with respect to the other ilaments in the cylindrical surface of the cathode, hence obviating the diiculties of warped wires, caused by non-uniform expansions of the wires. In addition each phase group can expand independently of the other, thus accommodating unequal expansions between groups due to un balanced phase voltages.

It has been found that discs 3, when made or some ceramic materials, tend to crack upon sudi,

den heating. A radial slot formed from the inner to the outer peripheries of thefdisc apparently prevents strains due to heat shock and eifectively prevents this cracking.

The cathode is easily assembled. The two legs of the wire spacers are sprung slightly to thread the ends of the wires into the spacer holes from opposite sides of the spacer, whereupon the ends civ the wires are bent over or upset to prevent their disengagement. Each filament wire is given slight off-set bends at the points where the bights oi' thespacer wires 9 engage the lament and then the filaments are threaded through the loops of the spacer wires. lThe supporting post is then passed through theholes of the aligned spacer discs and the entire cathode assembly mounted on its lead-in conductors in the tube header. Finally the connectors and filament ends are welded together and the finished cathode is mounted in its envelope.

Good results have been obtained in constructling cathodes according to my invention, for

evacuated transmitter tubes designed for high power and` high frequency. The laments are each tungsten rodsA .0515 inch in diameter andV 8.75 inches long. Twelve or" the wires are arranged in a cylinder 1.750 inches in diameter and are stiiiened through the ceramic spacers and wire braces by a molybdenum support post .25,0 inch in diameter, each phase group of four filaments drawing 141 amperes. The three-phase operation of my filament causes a negligible hum.

My improved cathode rigidly holds its position with respect to the other electrodes, does no-t change in size or shape during operation,zis easy to construct and is reliable in operation.V

I claim:

l. A cathode comprising a plurality of straight filament rods, said rods being' arranged in a cy` lindrical surface, a stiff supporting post disposed along the axis of the cathode cylinder and terminating short'of one end ofv the cylinder, brace wires insulatingly attached to said rod and to said laments, and flexible metallic connectorsV nector in a plane perpendicular to said post and spaced from the end of the post, flexible legs of the connector being electrically and mechanically connected to the ends of said iilament rods,

3. A cathode comprising a support post, a plurality of straight iilament rods parallel-to and arranged around said post, a disc of insulating material, smaller in diameter than circle of rods, coaxial with and slidable of said post, a brace wire, the wire being formed into a V, the bight `oi the wire being attached to one of said iilaments and the ends of the legs of the wire being attached to circumferentially spaced points on said disc.

' ll. 'A cathode comprising a straight lament rod, a supporting post parallel and spaced from said rod, means for holding said rod in xed spaced relation with said post, comprising an insulating disc on and coaxial with said post, and a wire brace with two relatively stii legs forming a V, the bight of the Vat the junction of the two legs being attached to the rod and the two ends of the legs being attached to circumferentially spaced points on the disc to prevent radial or circumferential displacement oi the rod with respect to the disc, yet to permit free longitudinal movement of the rod.

5. A cathode comprising a rigid supporting post, an insulating disc coaxial with and slidable upon said post, a brace wire formed'into a V with the ends of the Wires engaging circumferentially spaced holes in the discfand with the bight of the J lying in the plane of the `disc radially beyond the periphery of the disc, and a iilament rod l, passing thro-ugh the bight of the brace.'

6, A cathode comprising a plurality of straight filament rods, said rods being arranged in aA cylindrical surface, said rods being divided into groups with equal numbers of rods, the nlaments of one group being electrically and/'mechanically connected together at one end of the cathode.

7. A cathode comprising aplurality or" straight .filament rods, said rodsbeing arranged in a cylindrical surface, said rods comprising a plurality of electrically independent groups, a plurality ci parallel sheet metalrconnectors perpendicular to said rods, each connector having legs connected to each rod ofv one group, said connectors Abeing spaced longitudinally ofthe rods and mechanicallyindependent of each other t0 permit freedom of movement of each group of rods with respect to the other groups.

8. A cathode comprisingja plurality of parallel llament rods arrangedl in a cylindrical surface, a thin sheet metal connector perpendicular to said rods, the connector having aradially exy tending leg for each rod, each connector leg having a fold intermediate its ends, the `outer end oi the leg lying parallel to and against the side of the rod and being connected electrically and mechanically to the rod.

9. A cathode comprising a plurality'of parallel cylindrically arranged lament rods, Imeans for connecting the ends or" therodsat one end of the cathode comprising athinsheet-metal connector having radially' extending legs, each leg being bent into a plane parallel with the rod to which it is attached and a metal clip snapped overthe end of the rod and connector leg to hold the rod against the connector leg, the clip, rod andv connector leg being Welded together.`

ARTHUR K. WING7 Je. 

